This invention relates to gas burner controls for furnaces and the like, and in particular to a new and improved pilot burner gas ignitor and main burner valve controller. This system utilizes a pilot burner flame sensor and a control circuit for switching the main burner solenoid valve and the pilot burner spark ignitor circuit.
A typical system of this type is energized when the electrical contacts of a thermostat close in response to a drop in temperature of the area being heated by the gas furnace. When the thermostat switch closes, the pilot burner valve is opened and the spark ignitor circuit provides sparking at the pilot ignitor electrodes and the gas at the pilot burner should ignite. The flame sensor and control circuit detects the existance of the flame and actuates a switching circuit to energize the main burner valve and turn off the spark ignitor circuit. If flame outage occurs, the flame sensing circuitry will detect the absence of flame and close the main burner valve, while at the same time turning on the spark ignitor for reigniting the pilot burner.
Systems of this general type are known, and one such system is shown in U.S. Pat. No. 3,986,813. Other known systems are discussed in said patent.
However, there is a problem with the prior art systems. There is a possibility that the pilot burner will not ignite eventhough the pilot burner valve is open and the ignitor circuit is producing sparks. Under these circumstances, gas continues to flow from the pilot burner. When the fuel is natural gas, there is little problem, since this gas is lighter than air and the unburned gas goes up the flue. However, fuels which are heavier than air such as propane and butane are also being utilized. Under the situation referred to above, the unburned gas being heavier than air will collect in the area around the burners and there is a possibility that this fuel would be ignited by the sparking of the ignitor circuit, producing an undesired explosion.
Therefore, it is an object of the present invention to provide a new and improved ignition control system which will limit the spark ignitor action to a predetermined time, regardless of other conditions of the control system. A further object is to provide such a new and improved control system having fail safe characteristics so that the protection against continuous ignitor operation is achieved eventhough there is failure in the control components.